A human-portable hydroelectric generator that weighs about 30 pounds and generates 500 watts of power may soon be a new option for off-grid power.Developed by Bourne Energy of Mailbu, California, the Backpack Power Plant can create clean, quiet power from any stream deeper than 4 feet.The company showed off its more-rugged, militarized version of the Backpack Power Plant at the Cleantech Forum in San Francisco last week. Bourne Energy CEO Chris Catlin estimates the system will cost $3,000 after it goes into production.